Despite the fact that pit coal is one of our most plentiful and cheapest energy producing raw materials, it has so far been used only to an extremely limited extent as a reducing agent in the manufacture of sponge iron. This situation persists despite the favorable relationship between price and energy content with respect to pit coal.
Conventional processes for the manufacture of sponge iron in which coal is used as a reducing agent are primarily the following:
a. The rotary furnace method in which pit coal is used together with the ore to be reduced, in an inclined rotary furnace. The difficulty with this method is that, mainly due to kinetic energy, it is necessary to work with relatively high temperatures, preferably 1000.degree. C., which causes considerable problems with clogging and the accumulation of material in the reaction chamber. PA1 b. The use of a shaft furnace combined with equipment for gassification of coal, which is based on partial combustion. The drawback with this known method is primarily the extremely high investment cost for the gassification equipment and also the exceptionally high energy consumption. PA1 c. The method, such as is disclosed in Swedish Pat. No. 73 04 322-5, of directly gassifying coal in solid form using a plasma generator. The drawbacks of this method are that the supply of coal must be extremely accurately adjusted and for some grades of coal there are problems in handling the ash. Moreover, the gas produced has a hydrogen content which is lower than the ideal for reduction purposes.